1. Field of the Invention
The field of art to which this invention pertains is chemicals for use in enhanced recovery of crude oils from subterranean formations. The present invention resides in a specific method of treatment of a hydrocarbon polymer sulfonate so as to render that material more tolerant of divalent cations especially calcium when injected into a subterranean formation by reducing precipitation of materials caused by reactions with divalent ions present in the connate water in the formation.
2. Description of the Prior Art
There is much prior art relating to the use of polymer sulfonate as surfactants in enhanced recovery operations where crude oil is recovered from subterranean formations. U.S. Pat. No. 3,714,062, issued Jan. 30, 1973, and having as inventors Warren S. Askew and H. R. Froning relates to branched chain sulfonates for use in solubilized oil-water solutions for miscible water flooding. Specifically a solubilized oil-water mixture of a polymer sulfonate is mixed with cosurfactant and brine and injected into a subterranean formation. Enhanced recovery of crude oil present in the formation occurs. Normally this crude is not recovered when using straight water flooding techniques. This patent however does not recognize the problem associated with certain branched chain sulfonates in that precipitation of materials occurs when such sulfonate materials are contacted with reservoir systems which contain connate water having high concentrations of divalent ions, especially calcium. This phenomenon occurs even though the surfactant and crude give miscible mixtures.
Other patents which may be of interest in this area include U.S. Pat. No. 2,160,343 issued in 1939 and U.S. Pat. No. 3,506,070 issued in 1970.
Relevant classes which may be of interest for obtaining other art include U.S. Class 252-308, U.S. Class 252-353 and U.S. Class 166-273.